There is evidence that girls with ADHD differ from boys with ADHD most strikingly in 1) academic and social-emotional and 2) neurobiological features. Building upon previous research experience concerning neurobiological features of boys with ADHD, this proposal focuses on 2) neurobiology of girls with ADHD, with plans to derive data from quantitative volumetric/anatomic magnetic resonance imaging (aMRI) and assessments of executive behaviors, both motor/oculomotor and cognitive. To take gender into account, girls with ADHD will be compared with control girls as well as boys with and without ADHD. The age range for all 200 subjects (50 in each group) will be 9.0 through 11.5 years; in addition, even at this young age, Tanner staging will be taken into consideration. Anatomic MRI regions of interest will be frontal lobe, basal ganglia, and cerebellum. It is hypothesized that girls with ADHD will differ from boys with ADHD at the levels of frontal lobe (showing anomalous asymmetry only), and at the level of the basal ganglia (showing symmetrically smaller total caudate and globus pallidus volumes) while sharing with boys total cerebral and posterior inferior vermis reductions. Behavioral tasks, motor/oculomotor as well as cognitive, will be categorized into inhibitory control, response preparation, and working memory, functions thought to represent parallel frontostriatal and cerebellar interlocking circuits. It is hypothesized that girls with ADHD will be relatively more impaired in terms of response preparation and working memory than in terms of inhibition, a profile opposite to that of boys with ADHD. Gender-by-subtype interactions with respect to aMRI and behavioral datasets and the impact of emotional symptoms will be analyzed. Brain-behavior relationships as influenced by gender (modified by covariates as noted above) will be interpreted in terms of a neurodevelopmental model of ADHD.